This invention relates to an apparatus and method for improving the uniformity of pneumatic tires and to associated circuitry for controlling the apparatus.
The problem of tire non-uniformities has long been recognized by tire manufacturers and vehicle owners, and efforts to deal with such non-uniformities represent a significant part of the tire manufacturing process. The term tire non-uniformities generally refers to eccentricity of the tire, or free radial runout, wherein the tire periphery deviates from that of a perfect circle. The term tire non-uniformity also generally refers to radial force variations wherein the forces that are exerted radially between the tire and the road surface, under normal load, vary as the tire rolls along such surface. Other variables, not relevant to this discussion, are also included in the term non-uniformity.
A vehicle with one or more tires having the aforesaid non-uniformities usually provides a ride that is characterized by pumpiness, vibrations and noise. Since such conditions are uncomfortable and often exasperating, most tire manufacturers inspect or measure their tires for non-uniformities of the type described. Examples of methods and apparatus used in measuring such non-uniformities are disclosed in U.S. Pat. Nos. 3,550,442 and 3,719,813, which are assigned to the assignee of the present invention.
It has been found that minor non-uniformities of the type described do not provide an objectionable ride quality and do not adversely affect the wear of the tire to any great extent. Therefore, a tire is usually considered acceptable if it has non-uniformities that measure within a predetermined acceptable range. However, once the non-uniformity measurements fall outside the acceptable range, the cured tire is usually reworked in an apparatus for correcting such non-uniformities, generally known as a tire uniformity optimizer, hereinafter also referred to as a TUO
A TUO machine usually includes one or more grinding devices that remove tire material from a circumferential portion of the tread in a uniform circumferential band. Known TUO machines, as shown in U.S. Pat. Nos. 3,550,442 and 3,719,813, also perform non-uniformity measurements that precede the corrective grinding treatment of the tire. For example, such TUO machines include a wheel and axle assembly on which the tire to be evaluated is mounted, and also a test or load wheel that contacts the tire. The tire is forcibly held against the load wheel to apply a predetermined load on the tire. As the tire is rotated with the load wheel, the variation in radial force on the tire axle is measured. If the radial force variation is outside a specified acceptance range, some portion of the tread surface of the tire will usually be ground to modify or reduce the radial force variation.
A tire with non-uniformity measurements that are slightly outside the acceptance range will normally be ground only a slight amount. However a slight grinding of the tire often provides the tire periphery, at the tire shoulder for example, with an erratic surface appearance because the grinding is not extensive enough to remove sufficient material from the tire shoulder to esthetically blend the ground portions with the unground portions of the tire shoulder. The grinding pattern is thus irregular, which detracts from the appearance and marketability of the tire, even though the irregularly ground tire will provide a better ride quality than an unground, uncorrected tire which does not have an irregular appearance.
Known tire grinders such as shown in U.S. Pat. Nos. 3,963,427, 3,946,527, 3,935,676, 3,932,965, 3,914,907 and 3,841,033 treat a particular circumferential band of the tire by grinding in one direction only. Tires with tread patterns that extend axially (transversely) of the tire, rather than circumferentially thereof, such as all weather tires, snow tires, and mud and snow tires, have tread lugs or blocks that usually buckle or shift in the direction of rotation of the grind wheel when being ground. The tread lugs or blocks thus exhibit a shingled effect wherein the depth of grind varies on each tread lug or tread block over a circumferential hand of the tire. Thus, while a grinding treatment wherein the tire is ground in one direction furnishes some correction to radial force variations, the resulting shingled effect on tires with axially extending tread patterns increases the noise level of such tires and adversely affects the smoothness of ride.
It is thus desirable to provide a TUO machine and method that will uniformly grind a tread lug of a tire. It is also desirable to provide a TUO machine and method which automatically furnishes a generally uniform grinding pattern to a circumferential band of a tire without deleteriously affecting the uniformity of the tire even though the grind correction required by the tire would normally furnish the tire with an irregular grinding pattern.